1. Field of the Invention
The present invention relates to an electric actuator, particularly to an electric actuator suitable for lifting an aircraft leg.
2. Description of the Related Art
An example of a technique related to an actuator for lifting an aircraft leg is described in Japanese Unexamined Patent Application Publication No. 1999-59592. The leg-lifting device described in Japanese Unexamined Patent Application Publication No. 1999-59592 intends to achieve a simple layout by unitizing a leg-lifting mechanism including emergency leg-extension. The leg-lifting device includes the following members mounted in a common body: a pump as a hydraulic pressure source; a motor which drives the pump; a rod which extends in response to discharge pressure of the pump; and a mechanical lock mechanism which regulates extension of the rod.
Here, research and development of EMAs (Electro Mechanical Actuator) and EHAs (Electro Hydrostatic Actuator) are worldwide trends in the field of aircraft technology to eliminate the hydraulic system in order to realize a lighter aircraft. As far as lifting systems of lifting devices for aircraft legs are concerned, however, hydraulic actuators still remain as mainstream.
An example of an EMA developed for lifting an aircraft leg is illustrated in FIG. 6. An electric actuator 101 illustrated in FIG. 6 includes a cylinder body 84; a screw shaft 3 provided in the cylinder body 84 and rotated by an electric motor 23; and a piston rod 83 into which a screw shaft 3 is screwed. Further, a mechanical brake 81 is provided in the cylinder body 84. A side face of an end portion of the cylinder body 84 is provided with a limit switch 82.
The electric motor 23 is activated to cause the piston rod 83 to move linearly in an advancing direction (leg-extending direction) or a retracting direction (leg-retracting direction) in accordance with rotation of the piston rod 83. Here, the piston rod 83 moves in the leg-extending direction to cause a piston part 83a of the piston rod 83 to hit the limit switch 82. Upon receiving a signal, the electric motor 23 stops and the mechanical brake 81 is activated. The piston rod 83 is thus arrested and locked at a leg-extending position (stretched position). According to the electric actuator 101, no hydraulic pressure is utilized for driving the piston rod 83. This allows elimination of the hydraulic system which has been traditionally indispensable. Thus, a lighter aircraft is realized.